What you thought about people wanting to be somewhere else is true for most new students. It was true for me when I first went there. I was hoping to be put in one of the nicer looking/older halls of residence and was quite unhappy to be put in AMH. After a couple of months though I was already used to it and the people were so nice that I really started liking living there. This happened with many of my friends which ended up returning to AMH. Most people from other halls say "bad" things about it because it has an ugly look and it looks like a boat. It is true that it isn't the nicest hall, but the rooms are ok and I think in the end you will think it is good enough for you first year. Next year you can either apply to a nicer hall (like I am thinking of doing), or go into a private flat/house.
In terms of mixing 2nd years with other people the fact is that you get mixed with people from all courses and years. Though it is true that some areas are mostly first years and I knew of a full corridor which only had older people a couple of years ago. Most people will still be freshers since older students tend to go to private accommodation in later years.
I am sorry but I can't really help with the subjects question because I am studying Physics. Although I am going to the 2nd year my course is different. I have 2 modules in the 1st semester and 2 in the second. 2 of them are Maths modules and the other 2 are Physics modules.
One of the high points of the year are usually the fire drills. I don't know if the Warden is still the same, but we had quite a few when I was there and all of them at 3-4am (twice under the rain). Also, there tend to be some false alarms due to people not closing the kitchen doors while cooking, or trying to light candles in their rooms, etc...